need help in marlin

A person sent me a Marlin PI3 GT2560 file and said just verify and up load . .Well it crashed the GeeTech I3 Pro C Dual Head 3D printer . .
had a blank screen with 2 rows of small squares that were filled ! ! . . I dumped the stuff they said to use ( 1.0.1 Arduino and use windows to connect ) and went back to using the Linux ( Ubuntu 15.04 ) loaded Arduino IDE 1.6.5 and re verified and up loaded the file . . marlin.ino ( did verify before uploading ) got 99 % of things back on the panel
But at the bottom of the panel is a ERR : MINTEMP . . How do I fix this and how do I get the rest to work ? I have Repeiter-Host, Slic3r plus the Arduino IDE 1.6.5 loaded and talking to the printer via /dev/ttyUSB0 . . Need help in getting things running so I can actually make something via the printer
Using a marlin.ino file I did not make So something is wrong in the files it says to use . .

Just uploading any firmware (even if for the same ' brand') is a dangerous thing as you have noticed.

You will need to go through the Configuration.h file and make adjustments which are specific for your printer. If you can find the original firmware for your GeeTech, you can compare the Configuration.h file of that one to the new one. Using a compare utility like meld (http://meldmerge.org/ linux and windows versions) helps a lot. Once you have made the corrections, compile and upload again with Arduino, and test.

haha I can't even get the owners manual from them let alone the original firmware . . But I will ask them . .

They have a lot of this stuff on their forum. Check that out. That is where I found the G2s source.